In the process for production of acrylic acid or esters thereof by gas-phase catalytic oxidation, a bottom liquid discharged from a distillation column, which contains acrylic acid polymers, is usually fed to a decomposition reactor and treated therein. More specifically, in the decomposition reactor, the acrylic acid polymers are decomposed into valuable substances such as acrylic acid, acrylic esters and alcohols and then are recovered together with other low-boiling components. Since the decomposition reaction is performed in the predetermined range owing to the operational conditions of the reactor, a certain amount of the acrylic acid polymers tend to remain undecomposed. The undecomposed acrylic acid polymers are concentrated upon separating the other low-boiling components therefrom. As a result, the acrylic acid polymers are in the form of high-viscosity substances, and discharged as a bottom liquid from the reactor. The thus discharged high-viscosity substances are transported as industrial wastes in a high-temperature molten state to a storage tank through a pipeline.
Also, in the case where the bottom liquid discharged from the distillation column is already in the form of high-viscosity substances having the same composition as that of the bottom liquid discharged from the decomposition reactor, the bottom liquid discharged from the distillation column is transported as industrial wastes to the storage tank through the pipeline.
However, it may be extremely difficult to transport the high-viscosity substances discharged from the decomposition reactor or distillation column through the pipeline. For example, upon transportation of the high-viscosity substances, there are caused various troubles such as retention and clogging thereof in the pipeline. In order to improve a transportability of such high-viscosity substances through the pipeline, there is known the method of adding a solvent such as water, alcohols, ethers and carboxylic acids to the high-viscosity substances (Japanese Patent Application Laid-open (KOKAI) No. 2000-290225).
However, the addition of the solvent to the high-viscosity substances leads to increase in amount of a liquid to be transported, resulting in uneconomical industrial production process. In addition, when a large amount of the solvent is added to the high-viscosity substances, the liquid temperature of the high-viscosity substances tends to be lowered, thereby sometimes causing retention or clogging thereof in the pipeline.